This invention concerns heatable laminated multilayer insulating glass, also known as safety glass, which consists of at least two panes of glass held together at a distance with a spacer between them and with a gas-filled or evacuated interspace.
With such a multilayer glass, thin delicate electric conductors designed as resistance heating elements with the proper connections for passing an electric current through them are applied to the inner surface of one of the two panes of glass. Then the pane of glass is heated when an electric current is applied to these conductors, it absorbs heat and should release this heat to the air in the room of a building as a result of convection and/or radiation. In designing such a laminated multilayer insulating glass, the spacer must assure special properties. It must not only store the dessiccant as usual and assure access to the interior atmosphere in the interspace for the desiccant but must also have a sufficient rigidity, especially torsional strength, so the laminated multilayer glass can be handled but it must also provide adequate electrical insulation and insulation against the passage of heat.
Spacers made of aluminum, steel and plastic are known. Plastics are known to assure the best electric and thermal insulation. However, plastic does not have adequate strength or torsional rigidity and it also becomes brittle, especially due to the influence of changing temperatures and UV radiation, and it softens on exposure to high temperatures. Steel has sufficient strength but it has a relatively high electric conductivity and a high thermal conductivity. However, aluminum is the least suitable by its nature, although aluminum spacers have proven excellent for normal laminated multilayer insulating gas--i.e., unheatable glass--with regard to its shapability and strength. The thermal conductivity and electric conductivity of aluminum are incomparably higher than those of other materials (thermal conduction of aluminum/steel/plastics=200:52:0.22).
There are heatable laminated insulating glasses and plastic spacers. The disadvantages described here are simply accepted. This heatable laminated insulating glass cannot be expected to retain the required long-term properties.
Furthermore, a heatable laminated insulating glass with a spacer made of metal is also known, in which case a thick cushioning element made of a rubbery elastic substance is provided between the side surfaces of the spacer and the panes of glass. The function of this rubber elastic cushion is primarily that of sound insulation and secondarily it should also provide electric and thermal insulation. However, it has been found that although the sound insulation effect is good, the thermal insulation is inadequate and even the electric insulation is not optimum.
The purpose of the present invention is to create a heatable laminated insulating glass that can be handled very well and assures not only excellent strength and torsional rigidity in the case of spacers made of metal, but also assures extremely low thermal conductivity and an equally low electric conductivity.